Man from Atlantis (Blu-ray)

Mark Harris looks human, but he has incredible aquatic powers -- and one weakness: He can never be away from water too long. Still, he uses his amazing abilities for secret, highly dangerous underwater missions.

Description by OLDIES.com:

He's the lone survivor of a lost civilization...thrust into ours. A giant storm tosses ashore a being who is both human and a creature from the deep. Mark Harris is the name given to him by the astonished scientists who study and protect their remarkable find. Harris is equally astonished, a fish out of water eager to learn about us.

Patrick Duffy plays the Atlantean in the origin movie that (along with three more films) preceded the "Man from Atlantis" TV series. In this adventure, Harris uses his amazing underwater abilities to save mankind from a madman's plot to launch missiles from all the world's nuclear submarines.